#define _CRT_SECURE_NO_WARNINGS 1 		
#include<stdio.h>
int main()
{
	int a = 0;
	double num = 0;
	double sum = 0;
	int n = 1;
	for (a = 1; a <= 100; a++)
	{
		num = 1.0 / (a * n);
		n=-n;
		sum += num;
	}
	printf("%lf", sum);
	return 0;
}
